This application claims the priority of Korean Patent Application No. 2002-61047, filed Oct. 7, 2002, in the Korean Intellectual Property Office, the contents of which are incorporated herein in their entirety by reference.
1. Field of the Invention
The present invention relates to an optical disk system, and more particularly, to an apparatus and a method for scrambling and descrambling digital versatile disk (DVD) data in an integrated circuit for processing digital signals of a DVD system.
2. Description of the Related Art
Optical disk systems record data on optical disks, such as compact disks (CDs) or DVDs, and reproduce data recorded on optical disks. In particular, in reproducing digital data stored on an optical disk using an optical disk reproducer, a pickup device is used to radiate a laser beam on tracks of the optical disk, detect whether there are pits on the optical disk based on variation in the intensity of reflected light, and reproduce the digital data using the results of the detection. Such an optical disk reproducer is shown in FIG. 1.
FIG. 1 is a block diagram of a conventional optical disk reproducer. As shown in FIG. 1, a conventional optical disk reproducer includes a servo unit 110, a radio frequency (RF) unit 120, a digital signal processor (DSP) 130, a memory 140, and a MPEG unit 150.
The RF unit 120 converts light reflected from an optical disk 170 into electrical signals and outputs data signals and various error signals. The servo unit 110 converts the data signals and error signals output from the RF unit 120 into digital signals and controls the optical disk 170 in response to the error signals.
The DSP unit 130 receives signals which have been converted into digital signals by slicing in the RF unit 120, and performs various signal processing operations, such as EFM demodulation, error correction, and descrambling, on the signals. Here, data generated during each of the signal processing operations are temporarily stored in the memory 140. If data demodulated by an EFM demodulator 131 are stored in the memory 140, an error correction block 132 draws the EFM-demodulated data from the memory and performs error correction on the EFM-demodulated data. The error-corrected data are stored in the memory 140 and then are descrambled by a descrambler 133.
The data having been through such digital signal processing are MPEG-decoded in the MPEG unit 150, and then the MPEG-decoded data are output to a display or a speaker 160.
According to DVD standards applied to disks exclusively for being reproduced, data to be recorded on a disk are scrambled in accordance with the following. First, as shown in FIG. 2, scrambling bytes are generated. In order to generate such scrambling bytes, a linear feedback shift register (LFSR) 200 is generally used. The LFSR is a shift register constituted by fifteen bits and is set to a predetermined initial value in accordance with an initial setting value, as shown in FIG. 3. For example, when an initial setting value is ‘OH’, an LFSR 200 is initialized at ‘0001H’. When the initial setting value is ‘1H’, the LFSR 200 is initialized at ‘5500H’. In general, the initial setting value used to determine an initial value of the LFSR 200 sequentially changes sectorwise. Among the fifteen bits of the LFSR 200 shown in FIG. 2, eight lower bits R1 through R8 are used as scrambling bits.
The LFSR 200 shown in FIG. 2 performs an XOR logic operation on an eleventh bit R11 and a fifteenth bit R15 and inputs the result of the XOR logic operation in a first bit R1. Thereafter, the fifteen bits R1 through R15 are shifted one by one. The XOR operation and the shifting operation are alternately performed. The values of the first through fifteenth bits R1 through R15 of the LFSR 200 obtained after performing the XOR logic operation and the shifting operation eight times are shown in FIG. 4. Among the first through fifteenth bits R1 through R15 shown in FIG. 4, the eight lower bits R1 through R8 are used as scrambling bytes. Scrambling is performed by performing an XOR logic operation on data and the scrambling bytes, as shown in Equation (1).SD=UD⊕SB  (1)
In Equation (1), UD represents data before being scrambled, SB represents scrambling bytes, SD represents scrambled data, and ⊕ represents an XOR logic operation.
In order to retrieve the original data from the scrambled data, the scrambled data is descrambled. Descrambling is performed by performing an XOR logic operation on the scrambled data and the scrambling bytes, as shown in Equation (2).UD=SD⊕SB  (2)
In order to obtain the scrambling bytes, a bitwise operation has been performed in the prior art. According to conventional techniques, 8 clock cycles are taken to obtain one scrambling byte by performing a predetermined operation on one bit every clock cycle.
However, memories currently adopted in most DVD systems are mostly synchronous DRAM devices operating at a DVD speed of ×16. A device operating at a speed of ×16 means that 16 bits are simultaneously input to or output from the device. Accordingly, scrambled data from a memory can be operated on 16 bits at a time. Accordingly, if a scrambling byte is generated so that 16 bits are generated every clock cycle, the speed of scrambling and descrambling data will increase.